International demand for lighter ships with lower fuel consumption is on the rise. One possibility lies in the increased use of fibre-reinforced composite materials. Documenting the fire safety of such solutions presents a considerable challenge, and DBI has risen to meet this challenge.
As themes such as sustainability and climate change have made their way onto the political agenda, the shipbuilding industry is looking more to ‘green ships’ as the solution to global transport with reduced emissions of CO2, SOx and NOx. The hope is to develop and use environmentally and climate-friendly technologies that increase ships’ energy efficiency and reduce operating costs.
The new efforts involve a number of technologies, such as low-emission engines, new fuel types, heat recovery and the optimisation of ships’ trim. Weight reduction is another factor that is a fundamental means of lowering fuel consumption.
– Internationally, we’re seeing a demand for lighter ships and weight reduction from many sides. There’s no doubt that a snowball effect is underway, so we have to find materials and principles that can make ships lighter, says civil engineer Dan Lauridsen of DBI.
Bringing about a reduction in ship weight primarily involves manufacturing vessels with new materials such as FRP (fibre-reinforced plastic, e.g. fibreglass or carbon fibre) or light metal alloys. However, these approaches present new challenges as maritime technology is characterised by caution and tradition due to safety concerns, which typically has resulted in a preference for steel and non-flammable materials in general.
– In Denmark we’ve opted for a cautious approach in the use of FRP. When used in a ship’s superstructure, FRP cuts down on a lot of weight. We are, though, moving ahead slowly but surely because we’re ultimately dealing with people’s lives here, and we need to be absolutely sure what the new materials mean in terms of fire safety, Lauridsen explains.
Advantages of FRP
The benefit of using FRP in shipbuilding lies in the fact that the composite materials, when compared to steel, have a favourable strength-weight relationship.
The drawback is that FRP is flammable to a certain degree, and smoke formation can be a problem. As such, FRP cannot be used to fully replace steel. The material’s fire safety properties are far too varied and numerous, which is why it is necessary to examine the specific design of the overall solution.
It is thus possible to achieve significant weight reduction by using FRP for ship areas such as interiors, installations and insulation. Furthermore, FRP may also be used in sandwich constructions in which flammable materials are packed in between non-flammable types. For the time being, the industry’s focus is on utilising FRP to reduce the weight of ships’ superstructure.
SOLAS Chapter II-2: Prescriptive fire safety requirements
At the executive level, there are both national and international regulations that apply to ships’ fire safety. The international rules were developed by IMO and are part of the SOLAS (Safety of Life at Sea) Convention. Fire prevention, detection and extinguishing are discussed in Chapter II-2, which includes a number of detailed sections on various fire safety matters. Furthermore, different ship types, such as high-speed crafts (HSC), can be subject to special rules.
SOLAS Chapter II-2 represents prescriptive requirements for a ship’s construction and level of fire safety. These regulations are based on extensive experience from past fires, and the prescriptive approach is intended to mould requirements in such a way that the same hazardous situations do not occur again.
Fundamentally, SOLAS thus seeks to limit the use of flammable materials, as they have been a significant factor in many past maritime fires. An unintentional consequence, however ,is that SOLAS Chapter II-2 makes it difficult to develop new solutions using lighter materials, which are often more or less flammable.
SOLAS Regulation 17: Driving force or hindrance
The other initiative, fire safety engineering, is performance-based and is rooted in a more holistic safety design based on risk assessment. In this approach, the freedom to use new materials and designs is greater; on the other hand, builders must be able to document a satisfactory level of safety, which can be difficult.
Fire safety engineering became an alternative to the prescriptive requirements in 2002, when SOLAS was expanded by implementing the so-called Rule 17. With it, SOLAS now permits alternative methods for documenting onboard safety.
– SOLAS Regulation 17 can be used for flammable composite constructions provided builders can document that the level of fire safety is not lower than it is with steel ships built in accordance with prescriptive requirements, Lauridsen says.
Regulation 17 has, however, been used much less often, as both the technical safety analyses and appertaining governmental approvals are very complex, time-consuming and, as a result, expensive.
– We should therefore be asking ourselves whether Regulation 17 can realistically promote the use of new materials as the foundation for constructing green ships, or whether we need to see rule changes if the use of FRP or other new shipbuilding materials is to become a reality, Lauridsen states.
A need for new methods
One navigable way forward is to develop a number of standard constructions with FRP or other lightweight materials which, by applying fire safety engineering approaches, can be proven to be fireproof and thereby used and approved in accordance with SOLAS Regulation 17. This would make the fire safety documentation process a more manageable task, as it would no longer entail conducting costly and comprehensive fire testing. It would furthermore remove the barriers to innovation that currently exist in the traditional and experience-based, prescriptive approach.
– Before this becomes a reality, we have to overcome the general lack of knowledge. We don’t know enough about the fire safety properties of FRP and other new materials, just as we don’t know enough about the consequences of an increased use of FRP in ships. Furthermore, we need an analysis to be conducted of which parts of the ship’s structure, components and materials would most benefit by being converted to FRP, when compared with a comprehensive risk assessment, Lauridsen concludes.